This invention relates to C-arm apparatus and, in an important aspect, to mini C-arm systems such as are used for fluoroscopic imaging of a human patient's extremities and for other medical diagnostic purposes. More particularly, the invention relates to mini C-arm imaging apparatus incorporating new and improved locking mechanisms for holding the C-arm stationary in a selected position relative to C-arm supporting structure.
Mini C-arm imaging systems are well known and widely used in present-day medical practice, e.g. to provide fluoroscopic images and/or bone mineral density measurements of a human patient's extremity such as a wrist, hand, ankle or foot. One example of such mini C-arm apparatus is described in copending allowed U.S. patent application Ser. No. 08/794,615 filed Feb. 3, 1997 (in which the issue fee has been paid), the entire disclosure of which is incorporated herein by this reference. Another example is the apparatus described in U.S. Pat. No. 5,627,873, the entire disclosure of which is also incorporated herein by this reference.
As set forth in the allowed application and patent just cited, a mini C-arm system of the type herein contemplated includes a rigid C-shaped track continuously curved along an arc of a circle, with two opposed ends spaced apart by a gap and respectively carrying an x-ray source and an x-ray detector that face each other across the gap so that x-rays emitted by the source are incident on and detected by the detector. The source and detector are so arranged that when an object such as a human extremity is interposed in the gap and irradiated with x-rays from the source, the detector produces data representative of characteristics of the interposed object. The produced data, by way of illustration, may be displayed on a CRT as a fluoroscopic image of the object, or may be used (as the aforementioned allowed application Ser. No. 08/794,615 describes) to measure bone mineral density (BMD) of bone in the extremity.
The C-arm track is slidably mounted in a support member so as to be movable, relative to the support member, along a circular path substantially coincident (i.e. concentric) with the arc of curvature of the track. By such sliding movement, the x-ray source and detector can be moved rotatably about the center of circular curvature of the C-arm track. The support member, in turn, is pivoted on the distal end of an arm (or, preferably, an articulated arm assembly including two or more sections movable relative to each other) having a proximal end pivotally secured to a base. The pivotal interconnections between the support member, arm or articulated arm assembly, and base, together with the provision of sliding rotary movement of the C-arm relative to the support member, afford a plurality of modes of movement of the source and detector, including rotation about various differently-oriented axes, as desired to enable optimum positioning of the x-ray source and detector in relation to an object such as a patient extremity which is to be imaged and/or otherwise examined with the mini C-arm device.
Advantageously the various interconnections, pivots and articulations permit relatively easy movement, to facilitate positioning of the source and detector by a user such as a physician. Once the source and detector have been moved to a selected location and orientation, however, it is important that they be held fixed in position for the duration of irradiation of the patient. To this end, and again as shown in the aforementioned application and patent, it is known to provide means manipulable by the user for releasably locking the C-arm in relation to the support member and for releasably locking the pivotal joints. As the aforementioned patent also describes, the mini C-arm track, with its source and detector, may be mass balanced about the center of curvature of the track to aid in stabilizing the C-arm at any desired position relative to the support member, although this mass balancing does not obviate the provision of locking means. Locking means heretofore used to hold the C-arm track fixed in relation to the support member have typically been screw mechanisms carried by the support member for bearing frictionally, when tightened, against a surface of the curved track.
In use of a mini C-arm x-ray system to image or otherwise examine a patient's extremity, it is customary to place a surgical drape around the source and detector and the patient's extremity to maintain sterility during the examining procedure. When the C-arm or the entire support mechanism is rotated during positioning, the drape may accidentally catch and pull on the locking mechanism, loosening it sufficiently to permit the C-arm track to slide relative to the support arm. Such dislodgment of the C-arm track, source and detector from a preset position relative to the support member (e.g., during adjustment of one or another of the pivoted joints associated with the articulated arm assembly) is highly undesirable, causing inconvenience and loss of time.
Moreover, physicians using a mini C-arm system often want to employ the locking mechanism to apply light friction or drag on the C-arm track during the positioning phase of an examining procedure, so that the track will remain in a tentatively selected position but can be slidably displaced (relative to the support member) by manually applied force at a later stage in the positioning phase. With a conventional screw-type locking mechanism, it is difficult to manually fine-tune the tightening of the screw so as to provide such light drag.